Editing Phased array (section)

=== Fixed phased array ===
[[File:Antenna-tower-collinear-et-al.jpg|thumb|130px|An antenna tower consisting of a fixed phase collinear antenna array with four elements]]
Fixed phased array antennas are typically used to create an antenna with a more desirable form factor than the conventional [[parabolic reflector]] or [[cassegrain reflector]]. Fixed phased arrays incorporate fixed phase shifters. For example, most commercial FM Radio and TV antenna towers use a [[collinear antenna array]], which is a fixed phased array of dipole elements.

In radar applications, this kind of phased array is physically moved during the track and scan process. There are two configurations.
:* Multiple frequencies with a delay-line
:* Multiple adjacent beams

The [[SPS-48]] radar uses multiple transmit frequencies with a serpentine delay line along the left side of the array to produce vertical fan of stacked beams. Each frequency experiences a different phase shift as it propagates down the serpentine delay line, which forms different beams. A filter bank is used to split apart the individual receive beams. The antenna is mechanically rotated.

[[Semi-active radar homing]] uses [[monopulse radar]] that relies on a fixed phased array to produce multiple adjacent beams that measure angle errors. This form factor is suitable for [[gimbal]] mounting in missile seekers.